Environmental pollutants typified by dioxins are found almost everywhere on Earth today. They are also known to exert effects on fishes living in polluted ocean areas. They are considered to have no direct effects on health if present in trace amounts but, nevertheless, the ingredients to be ingested by humans as foods or feeds desirably contain the least amounts of environmental pollutants.
Marine product oils, for example, fish oils contain highly unsaturated fatty acids such as EPA (eicosapentaenoic acid, C20:5, n-3, all-cis-5,8,11,14,17-eicosdapentaenoic acid) and DHA (docosahexaenoic acid, C22:6, n-3, all-cis-4,7,10,13,16,19-docosahexaenoic acid). Being known to have various physiological functions, EPA and DHA are used as ingredients of medicines, health foods, foods in general, feeds and the like. Various purification steps are applied to make use of the EPA and/or DHA in marine product oils.
Non-Patent Document 1 discloses removing the insecticide DDT and its metabolites from fish oils by molecular distillation. Non-Patent Document 2 discloses that chlorinated hydrocarbons and free fatty acids can be removed from fats or oils using vacuum stripping or thin-film distillation. Non-Patent Document 3 discloses using physical refining and molecular distillation in order to remove free fatty acids and other undesired substances from oil compositions.
Patent Document 1 and Non-Patent Document 4 each disclose a method for reducing the quantities of environmental pollutants in a mixture containing fats or oils which comprises the step of adding a volatile working fluid to the mixture and the step of subjecting the mixture to at least one stripping process together with the added volatile working fluid.
Non-Patent Document 5 discloses that highly unsaturated fatty acids are decomposed thermally when fish oils are deodorized at high temperatures.
Non-Patent Document 6 discloses removing dioxins, free fatty acids and cholesterols from fish oils by short path distillation so as to make them suitable for use as feedstocks for ethyl esters.